This invention relates to well logging and, more particularly, to the means and method for providing a direct visual indication of the presence of a predetermined constituent of an earth formation.
Various techniques and apparatus are now used for the purpose of well logging to study the properties of subsurface formations to determine the presence or absence of given naturally occurring substances, such as oil. The principal techniques presently being used either involve the taking of a core sample from the bore hole and subsequently chemically analyzing it, or measuring the radioactive properties of the subsurface formations. In either case the measurement techniques are complex, and the means by which results are actually determined are similarly complex. Moreover, the results of any such measurement are not produced immediately, and a relatively long period of time is required before a determination can be made regarding the content of the subsurface formations being examined.
Using core sample techniques it is necessary to physically remove a portion of the subsurface formation being examined to what is substantially a laboratory environment to permit a chemical analysis. There the core sample is chemically analyzed to determine its constituents and, particularly, to determine the degree of presence of the substance being sought, such as oil. Obviously, this technique is cumbersome, and presently available methods of chemical analysis of such core samples require significant periods of time before completion. In many circumstances, particularly in an oil drilling environment, such losses of time are economically disadvantageous.
The other major technique for well logging involves the use of means for studying the radioactive properties of the subsurface formations in question. This technique could involve the measurement of natural radioactive properties, or it could involve measurements wherein the radioactivity is artificially induced. The means by which this radioactivity is measured are complex, expensive and often unreliable in the harsh environment in which they must be used. For example, in the case where gamma radiation is being measured, crystals must be used which respond to the gamma radiation to thereby produce light energy which is subsequently converted to electrical energy having a complex wave form. It is then necessary to rigorously analyze the wave form content of the aforementioned electrical signal, and this analysis often requires the aid of a computer. It is only after this complex mathematical analysis of the electrical wave form generated as described above is completed can there be made a determination as to the presence or absence of the substance being sought in the earth formation being analyzed. Obviously, this technique requires complex and expensive apparatus and requires complex and time-consuming analysis procedures before a conclusion can be reached.
It is, therefore, an object of this invention to provide a means and method for examination of earth formations in, for example, a bore hole which will provide a direct and immediate indication of the presence or absence of a given substance in the formation.
It is another object of this invention to provide a means and method for the in situ examination of earth formations penetrated by a bore hole which utilizes relatively simple and inexpensive apparatus and requires no subsequent chemical or mathematical analysis.
An additional object of this invention is to provide a means and method for the examination of earth formations in a bore hole which are relatively simple to operate and which do not require the presence of highly skilled personnel to carry out the method nor to receive and understand the results.